Influence of Temperature and Photoperiod on Flowering and Tuberous Root Formation of Pachyrrhizus tuberosus

P. tuberosus, a native species of the Amazon region, was cultivatedunder different thermal regimes and photoperiods in an attemptto relate these stimuli to flower initiation and tuberous rootformation. It is shown that P. tuberosus is an intermediate-dayplant (flowers only under photoperiods above 9 h and below 16h). With regard to tuberization P. tuberosus may be considereda short-day plant: tuberization occurs only in photoperiodsbelow 16 h. High thermal regimes 30/25 C (13 h day/11 h night)delay and reduce flowering and completely inhibit tuberous rootformation. Thermal regimes of 25/20 C and 20/15 C (13 h day/11h night) were the most suitable for flowering and tuberization. Pachyrrhizus tuberosus, yam-bean, flowering, tuberization